Yale astrophysicist on unlocking the mystery of black holes and dark matter

In 2019, the first up-close image of a black hole was recorded. And yet, so much about them, their bizarre properties and the role they play in the universe remains a mystery. The distinguished Yale astrophysicist Priya Natarajan dives into black holes and dark matter in her lecture and book: Mapping The Heavens.

Author of Mapping the Heavens, Priya Natarajan, explores radical scientific ideas unveiling the Cosmos

The silhouette of the supermassive black hole that resides in the centre of the galaxy M87, outlined by emission from hot gas swirling around it under the influence of strong gravity. This image was produced by the Event Horizon Telescope Collaboration on April 10, 2019. (National Science Foundation via Getty Images)

*Originally published on May 15, 2020.

It took more than 40 years for black holes to be proven real and not mere mathematical curiosities. They became defined as a region of space from which nothing can escape. It wasn't until 2019 that the first close up image of a black hole was reported. 

And yet their bizarre properties and the role they play in the universe remains a mystery.

Distinguished theoretical astrophysicist Priya Natarajan dives into black holes and dark matter in the fifth annual Dan MacLennan Memorial Lecture in Astronomy, held at St. Mary's University in Halifax, Nova Scotia.

"One of the reasons I love black holes and I'm drawn to them is because they represent the limit of human knowledge," says the Yale University professor.

Natarajan's lecture is based on her book Mapping the Heavens: The Radical Scientific Ideas That Revealed the Cosmos, published by Yale University Press.

Here is an excerpt from the book:

Our map of the cosmos has changed dramatically in the past hundred years. In 1914, our own galaxy, the Milky Way, constituted the entire universe — alone, stagnant, and small. Cosmological research still relied fundamentally on "classical" conceptions of gravity developed in the seventeenth century. Now, we see the universe as a dynamic place, expanding at an accelerating rate whose principal mysterious, constituents dark matter and dark energy remain unseen.

The elements in the periodic table that constitute the stars and us contribute an insignificant 4% of the total inventory of the universe. Yet we have a remarkably detailed if incomplete understanding of the universe. Modern physics and the triumphs of general relativity have shifted humanity's entire comprehension of space and time. We have confirmed the existence of other planets orbiting other stars in our galaxy. We question the existence of other universes. This is remarkable scientific progress. 

A map of the heavens - our cosmic view then - from The Celestial Atlas of Andreas Cellarius published in 1660. (Submitted by Priya Natarajan)

Cosmology, perhaps more essentially than any other scientific discipline, has transformed not only our conception of the universe but also our place in it. This need to locate ourselves and explain natural phenomena seems primordial as registered in ancient creation myths. Myths helped humans deal with the uncertainty of violent natural phenomena, and share remarkable similarities across cultures. These super natural explanations evoke a belief in an invisible and yet more powerful reality, and they rely deeply on channeling our sense of wonder at the natural world. 

Our complex imaginations enabled us to envision entities that are not immediately present, and yet feel real. Take for instance, Enki, the Sumerian god of water whose wrath unleashed floods, or the Hindu god of rain and thunderstorms, Indra, whose bow was the rainbow stretched across the sky with a lightning bolt as his arrow. The most powerful myths are the ones that force us into taking huge leaps of imagination and yet help us remain rooted.   

The Nebra Sky Disk excavated from the Saxony-Anhalt region in Germany is dated to the Bronze Age (around 1600 B.C) and is one of the oldest surviving depictions of the night sky. (Submitted by Priya Natarajan)

In the beginning, the only instrument that humans had for observing the cosmos was their eyes. Mythos, not science, governed their interpretations, and they attributed the invisible, mysterious, superhuman forces that guided the planets and the stars to the actions of the gods. When the ancients looked at the heavens, they sought both utility and predictability. And much like we do today, they documented the cosmologies they created. They made maps. 
Today we use astronomical data to support or overturn astrophysical concepts and models, but in ancient times human understanding of the heavens had a more intimate connection to quotidian events.

Registering current celestial events was in the service of predicting future ones, but the ancients were not seeking to explain patterns or to arrive at their causes. Their goal was to record movements and to develop descriptions that would enable accurate future prediction. This is the root of astronomy-observation. Seeing and recording how objects move in the sky eventually gave birth to a science, even if the original explanation for these objects' movements was anything but scientific. This early tradition that centered on taking data from the night sky was crucial. It gave society an instinct — to connect our place on our planet to our location in the cosmos. 

Schematic showing how the presence of matter bends and alters the path of light rays in the universe. (Submitted by Priya Natarajan)

As a child growing up in India, I also felt this drive to locate myself in the world. My first guide was The Encyclopedia Britannica. Thirty-two volumes of the fifteenth edition, sitting on my parents' bookshelf, represented for me everything that was known at that time. I was enchanted: I immersed myself in ancient maps, maps that guided the voyages of exploration, and maps of the sky. I was transfixed by the stars. My personal cartographic adventure also gave me my first taste of scientific research. Programming a Commodore 64, I wrote code to generate the monthly sky map over Delhi for a national newspaper. Thus, began my love affair with the idea of discovery and exploration.

I meandered through physics, mathematics, and a smattering of philosophy during my undergraduate years at the Massachusetts Institute of Technology. My curiosity would lead me first to graduate study in MIT's Program in Science, Technology & Society before I headed across the pond to Cambridge for my Ph.D. in astrophysics. As a practicing scientist, I continually draw on my intellectual training in the history and philosophy of science to reflect more deeply on the process of scientific discovery and how it shapes the knowledge we produce.

Author of Mapping the Heavens, Priya Natarajan says she's always looking for gaps, or hints of exciting new physics that remain to be detected. (Yale University Press/Submitted by Priya Natarajan)

At its heart, my research as a theoretical astrophysicist, mapping dark matter and understanding the formation of black holes, is driven by the same sense of wonder and search for explanation of the universe as the ancients. I am still engaged in exploring the meanings of maps and how they anchor us, matters that first intrigued me as a girl in Delhi.

My own work exploits the bending of light from distant galaxies, gravitational lensing, to map dark matter that causes these deflections. I also work on understanding the formation and growth of black holes, these bizarre and enigmatic objects in the universe. The invisible has always had a hold on me.   


About the guest in this episode:

Priyamvada Natarajan is an astrophysicist and professor at Yale with a joint appointment in the Astronomy and Physics departments. She has made seminal contributions to our current understanding of the formation and growth of black holes and of the nature of dark matter by mapping it using gravitational lensing. She's a recipient of many awards & honours including the Guggenheim and Radcliffe fellowships. 

Natarajan is also the chair of the Division of Astrophysics of The American Physical Society and currently serves on the national Astronomy & Astrophysics Advisory Committee that advises NASA, NSF and DoE. She is deeply interested in interdisciplinary scholarship and is at present the Director of the Franke Program in Science and the Humanities. 

* This episode was produced by Mary Lynk.

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